THE UNITED STATES has settled into a siege of Panama, with Congress now having strengthened the sanctions the Reagan administration imposed last summer. This is a rare case where American conservatives and liberals alike find it both compelling and feasible to put pressure on a repressive, corrupt military regime. The sanctions entail an aid cutoff, elimination of the sugar quota and mandatory votes against development loans, and are perhaps the stiffest the United States has placed against any ostensibly friendly country.

But Gen. Manuel Noriega, the resident strong man, hangs on. He does it by mobilizing the anti-Americanism that is part of Panama's long, close tie with the United States. He milks the relatively advanced economy that has made Panama an exception to the general Central American bleakness. Most of all, he leans on the interest of the Panama Defense Forces, which he commands, in perpetuating their privilege. This is how he tries to defy not only the wishes of Washington but the desires of the majority of the Panamanians.

Over time, one has to hope, the will of the Panamanians will prevail, peacefully. Meanwhile, there is another kind of leverage that should be applied. It is the influence of other Latin democracies, especially those recently returned to democracy. They "should not forget," writes Panamanian opposition leader Ricardo Arias Calderon, ''that they demanded and obtained international solidarity in their efforts to establish democracy and to consolidate it. Reasons of state or unwillingness to parallel U.S. policy do not excuse reticence or indifference when human rights and democracy are at stake.''

Yet the Contadora Latins, setting themselves up as a permanent Latin caucus, have just allowed Panama's puppet president to sign their buttery appeal for ''peace, development and democracy.'' Military-ruled Panama is to sit on the verification commission set up to oversee Central America's advance toward peace and democracy. The Latin democracies, by treating an ugly military regime as their equal, betray Panama.